Re: PPC32: Boot regression on Nintendo Wii, after create_branch rework in 5.8

quoted

Do you have any hints on how to debug and/or fix this issue?

Thanks for bisecting and reporting.
The "Finalizing device tree... flat tree at 0xXXXXXX" message comes
from the bootwrapper so if that is the last output it must be crashing
pretty early.
Commit 7c95d8893fb5 ("powerpc: Change calling convention for
create_branch() et. al.") made a change to machine_init() in
setup_32.c which seems like it might be a likely culprit for causing
early crashing.
The branch that is created and patched is just for optimization, so to
see if that is in fact the problem it might be worth trying to boot
with a patch like below

diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
--- a/arch/powerpc/kernel/setup_32.c
+++ b/arch/powerpc/kernel/setup_32.c

@@ -87,9 +87,6 @@ notrace void __init machine_init(u64 dt_ptr)

        patch_instruction_site(&patch__memcpy_nocache, ppc_inst(PPC_INST_NOP));

-       create_cond_branch(&insn, addr, branch_target(addr), 0x820000);
-       patch_instruction(addr, insn);  /* replace b by bne cr0 */
-
        /* Do some early initialization based on the flat device tree */
        early_init_devtree(__va(dt_ptr));